As hobo joe says it's all personal preference really people may suggest either but it does not mean it's right for you. I ride motorbikes and the golden rule always is try it on before you commit to buying anything you don't want to be paying out and then realise you don't like the fit
With masks, the only way to tell is to try them on, and if you have the chance, borrow from a friend and play a couple of points with them. It is all to do with how they feel, the vision, how well you can hear, and how well team mates can hear you!
I am new to p8ballin and was looking to get i4. I was given the priveledge of trying them on and they are really comfortable. But I also have a set of valours. Which are ok. But again it's all preference
I've always had a pro flex and would swear buy them, comfortable and great vision, but I borrowed an I4 for NvS and they were really good also, the only downside I found was they were harder to hear ppl and they struggled to hear me because of the tighter fit around the mouth
I4's are great.......... Providing you like taking shots to the Chin, ears and forehead, they are very very small, I have them and if I wanted to shell out another £80 odd I'd get rid of them tbh, they are very easy to breathe in though, they sit perfectly on the nose which I found not many others out there do.
i tried the I4's and it was to tight for me, i would say they are better for people with a smaller head, not tries the proflex's yet... but my favourite is the Empire E-flex